Private lines are typically point-to-point communication channels provided by telecommunications (Telecom) carriers. Telecom carriers provision a fixed route on their network that creates a pre-defined point A to a point B communication channel. Unlike with Public Switched Telephone Network (PSTN) services, the telecom carrier of a digital network reserves network bandwidth to ensure the private line is non-blocking. The term non-blocking means service is always available and not affected by other network traffic. This differs from a standard PSTN dial tone line wherein the carrier receives dialed digits from the calling party, then routes the connection based on a dial plan, as a standard PSTN dial tone line has the potential for blocking during peak calling periods.
One of the primary forms of voice communications in the financial trading industry is a direct private telephone line. These private lines are often referred to as ring down circuits within the global financial trading community.
Types of Private Lines: Telecom carriers offer private line service in analog, digital time division multiplexing (TDM) and voice over internet protocol (VoIP) formats. However, the analog format was where the behavior and functionality of private lines was first defined and thus forms the basis for modernized digital TDM and VoIP service delivery by carriers.
Manual Ring Down (MRD) Lines: The term manual ring down refers to a specific type of signaling format and type of private line. This circuit type of private line lacks off-hook/on-hook signaling or talk battery from the telephone company. Historically, MRD's were provisioned by carriers by physically running copper wires from location A to location B or more commonly leasing these copper wire facilities from a local telecom access provider. Proper termination of MRD private line signaling on customer premises telephone equipment requires each of the two end points to be responsible for providing talk battery for their own phones and ring generators to ring the far end. In the United Kingdom these lines are also known as “gen-gen” representing the fact that there is a user provided customer premises equipment (“CPE”) ring generator on both sides of the telephone line.
In trading applications, these types of lines are typically used when one end or both ends of the line will be presented on a speaker that is always live. If the speaker is ever turned off or if the line is on a handset the other end will send ring voltage via a ring generator to ring the speaker that may be turned off or the handset that may be on hook.
This phone line is called “manual” ring down because the telephone set provides the user with the ability to send ringtone to the far end. A signal button is pressed whenever the user needs to ring the far end. FIG. 1 provides an overview of conventional MRD signaling.
A significant characteristic of MRD lines is that there is no line state. There is no way to know if either user is on-hook or off-hook other than by listening to hear if sound is being produced at the other end. This can result in one end ringing the other end even if the phone is already off-hook. This concept of “lack of line state” will be discussed below with respect to MRD emulation using SIP (Session Initiation Protocol).
Shout down lines: Shout down lines are identical to MRD lines in every way except that the CPE does not offer a ring generator for distant end signaling. These private lines are typically used between two parties engaged in shout-down communications that are always on. The advantage of shout-down lines is that connection is always engaged so each party can instantly communicate with the other without any physical interaction (similar to being in the same room with someone). FIG. 2 provides an overview of a conventional shout down connection between two parties. As shout down private lines are actually a version of MRD circuits, they share the common characteristic that there is no line state.
Hoot & Holler Lines: The previous MRD and shout down private line description is most commonly used for two-party point A to point B communications scenarios. Hoot & Holler lines were invented to support situations where more than two communicating party locations are required. In other words, three or more parties communicating in an open, always available conference call. Unlike point-to-point analog private lines that are traditionally delivered by the telecom carriers in a two-wire format similar to analog PSTN (dial tone) circuits, Hoot & Holler lines require separation of transmit/receive paths and therefore are delivered using a 4-wire circuit connection. Separating transmit and receive channels helps to prevent acoustic feedback and allows the use of separate transmit/receive (“TX/RX”) amplifiers to support an unlimited number of end point circuit terminations. Two wires are used for transmitting voice and two wires are used to monitor activity from any far end party. Another often used term for hoot & holler lines are junkyard circuits. Junkyard circuits use hoot & holler service to broadcast to other connected junkyards. The circuit is often times used to trade auto parts. FIG. 3 provides an overview of a conventional Hoot & Holler circuit. Similar to MRD and shout down private lines, hoot & holler circuits have no defined line state.
Automatic Ring down Lines (ARD): ARD circuits were developed to allow plain old telephone sets (POTS) and office telephone systems to access carrier private line services. The service provider supplies talk battery and ring generator. By design, ARD private lines have similar electrical characteristics as standard analog PSTN dial tone circuits. A distinction between ARD private lines and dial tone circuits is that the carrier does not offer dial tone on ARD private lines. Because ARD circuits are intended for point A to point B communications, dialing is not required. Simply the act of going “off-hook” is sensed by the private line provider. The private line provider then automatically rings the distant end, which is set when the private line is provisioned. FIG. 4 provides an overview of conventional ARD signaling. ARD circuits have defined line states. Detection of DC current flow on the two wire circuit allows the carrier to determine the on-hook or off-hook state of each termination point.
Private Line Automatic Ring down (PLAR): With one exception, PLAR lines are identical to ARD lines. PLAR circuits have an additional line supervision feature. Line supervision monitors the state of each end point of the private line and signals the distant end when the state of the local side changes. For example, when side-A hangs up the private line the network carrier signals side-B of this off-hook to on-hook state change. This signal is commonly referred to as a ‘wink’ and is transmitted by temporarily reversing voltage polarity on the wire pair or by temporarily interrupting the talk battery supply on the circuit. This additional supervision feature allows customer provided telephone systems to offer users more detail about the state of the private circuit connection.
Evolution of Digital Private Lines: During the 1990s telecom carriers introduced digital TDM service delivery. This offered carriers a way to expand the type and density of services that could be delivered to potential customers without having to upgrade the local access copper infrastructure into buildings. As digital trunks became available, a method of supporting private line functionality was also required over these digital transports. In the United States T1 digital trunks were used which relied on channel associated signaling (CAS). In Europe E1 digital trunks were deployed and also relied on CAS for signaling. The difference between T1 & E1 is not relevant to this discussion.
CAS represents a set of transmit and receive signaling bits per channel. Each TDM (multiplexed) channel is a voice circuit or the digital equivalent of an analog line. The result is a digital E1/T1 trunk that supports multiple communication circuits with signaling bits that determine the type of service delivered in each channel. The signaling bits are used to send and receive signaling actions to and from the distant end and service provider. The signaling format emulates the same signaling actions that are present on the analog circuits described previously in this background.
MRD emulation of digital E1/T1 trunks                Transmit signaling bits are used to send ring signal to the distant end.        Receive signaling bits are used to receive ring signal from the distant end.        
Unlike ARD & PLAR the carrier simply passes through the signaling bits and is not involved in signaling.
Shout down and Hoot & Holler Circuits emulation of digital E1/T1 trunks                Transmit signaling bits are static meaning that they don't change because no ringing or battery is ever signaled to the far end.        Receive signaling bits are static meaning that they don't change because no ringing or battery is ever sent from the far end.        
Unlike ARD & PLAR the carrier simply passes through the signaling bits and is not involved in signaling.
ARD & PLAR emulation on digital E1/T1 trunks:
Perspective of the private line phone:
Signaling bits are transmitted to indicate the following:                The phone is off hook and drawing loop current from the private line provider.        
Signaling bits are received and indicate the following:                A ring signal is being received from the private line provider.        A polarity reversal indicating that the far end went on hook. (PLAR only)        A loop current disconnect (battery disconnect) indicating that the far end went on hook. (PLAR only)        
Perspective of the private line provider:
Signaling bits are transmitted to indicate the following:                A ring signal is being sent to the private line phone.        A polarity reversal indicating to the private line phone that the far end it was communicating with went on hook. (PLAR only)        A loop current disconnect (battery disconnect) indicating to the private line phone that the far end it was communicating with that the far end went on hook. (PLAR only)        
Signaling bits are received to indicate the following:                Loop current (talk battery) is being drawn by the private line phone indicating that it is off hook.        
Evolution of private lines using VoIP Protocols: SIP is predominantly the VoIP protocol that is relevant to the disclosed technology. The next most popular VoIP protocol was H.323. H.323 and other VoIP protocols have been used for standard PSTN (dial tone) services but not for private lines. These VoIP protocols still exist today, but since 2014 SIP has been the predominant VoIP protocol for private line service delivery.
SIP Sessions for stateless private lines: SIP is a session protocol and assumes a session is set up between two endpoints. As noted previously; MRD, shout down, and hoot& holler circuits do not support an on-hook or off-hoot state. These lines do not have a state because they are always connected from the perspective of the provider. Therefore, these types of lines do not establish a session between each other. Thus SIP does not natively support these line types. The contradiction is that SIP is a session protocol that cannot adequately emulate an analog private line service that has no discernable state. This has led to customized implementations which are described in U.S. Pat. No. 8,599,834 and https://datatracker.ietf.org/doc/draft-beauchamp-private-wire/. These custom implementations mean that both ends of the line must implement the specific custom implementation in order to be compatible.
SIP Sessions for stateful private lines: PLAR and ARD have an on/off hook state and therefore can be emulated through the SIP protocol.
SIP Sessions and Signaling Paths: Analog and digital lines signal directly from one termination to another. In contrast SIP often uses SIP proxies. This is described in, among other places, http://datatracker.ietf.org/doc/rfc3261/?include_text==1. This signaling structure is sometimes referred to as the SIP trapezoid and is illustrated in FIG. 5. Modern phone systems terminate SIP on the phone system and not directly to the end user telephone connected to the phone system.
Private line service use in industry: Private lines are used in many industries. Examples are: financial trading, public safety, command and control applications, enterprise help desks, power industry communication, and more. While the description in this application will focus on the trading industry the technology is applicable to these other industries as well.
Financial Trading Industry: Private lines provide traders with a one to one connection between two firms. However, firms involved in trading need to connect with many counterparties. Therefore, traders typically require multiple private lines. Trading floors designed prior to 1970 required many telephones to be installed at each trading desk.
The turret system, also known as dealerboard system, was designed to connect a single phone to multiple private lines and allow users to access these connections through a single multi-button telephone. The turret is a specialized key telephone (http://en.wikipedia.org/wiki/Key_telephone_system#Key_system). Starting in the 1970s providers of these systems were AT&T Comcore, V-Band Systems, Tech Turret, IPC Systems, City Business Products (CBP)/British Telecom. Modern turret providers are IPC, BT-Syntegra, Orange Business Systems/Etrali, Speakerbus, IP-Trade, and a few others.
With the advent of the turret system, traders could trade as a collaborative team. These lines were no longer connections between two individuals but between teams of people at different firms. Private lines were terminated on line cards that offered many traders at a firm common access to services. Therefore, a calling party calls to a firm, without knowing who at the firm will answer. However, the service is improved because of the increased likelihood of an available trader to answer the call on the private line.
Limitations of existing technology: Private voice circuits are considered specialized services by telecom carriers and many carriers no longer offer these services. Today, the niche private line market is maintained by small specialized telecom companies that focus on financial trading services, and are often trading system (turret) providers as well. Unlike many other modern telecommunications services, existing private voice circuits have several undesirable elements:                Long provisioning timeframes        Expensive        Long commitment periods        IT staff involvement is required during provisioning and installation        
Network anatomy of a private line circuit: Connecting two firms with a single private line is a complex logistical process. There are three network components to be considered when a single private line is provisioned between two trading floor locations.
1. Local loop circuit from central office to trading location A.
2. Inter-exchange bandwidth across telecom carrier network.
3. Local loop circuit from central office to trading location B.
FIG. 6. illustrates the three network components that are required to provision a conventional point to point private line connection. Depending on the locations of the two end points of a private line, it can be necessary to use multiple network service providers to obtain the required connections between local circuits (“last mile”) and interexchange bandwidth (“long haul”). The coordination between telecom providers is often left to the customer, or to one of the local telecom providers if private voice circuits are a standard service offering.
Delivery of Private Line from the Carrier to the Customer Demarcation Point: Typically, telecom carriers deliver their services to customer premises over copper or fiber cabling systems. Tier 1 local access providers own and manage this infrastructure, while other service providers lease these building access facilities. In either case, the telecom service provider must install and manage their own service access points within a customer facility. This point is often referred to as the telecom demarcation or “demarc”. The telecom demarc is the wiring facility and connection point where customer provided equipment is interfaced to telecom carrier services. FIG. 7 provides a diagram that explains the interface between the network carrier demarcation point and customer premises interfaces.
Like traditional PSTN services, private line circuits are terminated on the service provider's demarc. The demarc includes wiring blocks with clear identification of all services by circuit ID. When delivered in an analog format, each private line is terminated on the demarc wiring block as a single pair of copper wires. This pair is often referred to as a “tip and ring” circuit. When the telecom provider delivers digital private line service the demarc requires two copper wire pairs that multiplex (TDM) many private lines together. This circuit is often referred to as a four wire TDM circuit. In the United States the telecom standard is to multiplex 24 circuits into a single TDM T1 circuit. In most other countries, a slightly different standard is used where 30 circuits are multiplexed into a single TDM E1 circuit.
Delivery from Customer Demarcation Point to the Customer Phone System: Once private line circuits are terminated onto the service provider's demarc they need to be interfaced to the customer's telephone system. Traditionally, the customer is responsible for the wiring of services from the Telco demarc to their own equipment. Copper wiring between Telco demarc and customer telephone system is often referred to as cross connect wiring. FIG. 8 illustrates the cross connect wiring requirements for analog, digital and VoIP private lines to be connected between network carrier and customer provided telephone system.
Financial trading firms often have hundreds of private line circuits that they use for communicating with counterparties. Therefore, they must maintain large wiring frames for cross connecting telecom services onto their telephone systems. The migration of private line services from analog to digital occurred during the 1990s. While analog services are still supported, most private line service providers and trading firms prefer digital service delivery because it simplifies the wiring, testing and management of private line services.
The customer is responsible for purchasing and equipping their telephone systems with the proper interface cards that will be compatible with the services offered by the Telco provider at the demarc. Most modern telephone systems that support private line service can be equipped with analog line interface cards for analog services and digital line interface cards for digital services.
When analog services are provided, each private line requires the customer to cross connect a pair of copper wires between the carrier's Telco block and analog line interface card. If digital services are offered the customer must cross connect four copper wires to a corresponding digital interface card.
Programming of telephone system to provision lines onto line interfaces: Once a private line has been connected via cross connects to the telephone system, the customer is responsible for programming the system to accept the service and to test whether the circuit is operating properly. Along with making sure the proper interface card is connected to the telecom provider's private line service, programming is required to make sure proper telecom signaling is assigned. While beyond the scope of this document, interface settings (i.e. circuit type assignment, bit signaling, voice and data channel assignments) must be properly programmed for each private line circuit connected on the telephone system before new service can be ready for testing.
Programming of telephone system to provision lines to buttons on users' phones: A private line circuit is uniquely designed to provide a dedicated voice channel between two locations. Each location can contain many individuals that need equal and often simultaneous access to the private circuit for the purpose of communicating with counterparties (other firm) and each other (same firm). Therefore, the termination and presentation of private circuits on the customer premises telephone system is also unique.
Typically, customer premises telephone systems are designed as private branching exchanges (PBX) that allow local users to access circuits in an unshared and contentious format. Users can access terminated telecom circuits, but normally do not share them at the same time. For incoming calls, PBX systems route circuits to individuals' extensions. For outgoing calling the PBX system allows users to contend for available outgoing circuits using dial access codes. FIG. 9 provides an overview of generic PBX system call routing features.
Using a branching exchange system to interface to private lines tends to defeat the purposeful design of the connection to provide shared simultaneous communications between users at each location. A key system design is a better telephone system to terminate and offer private lines to users.
A key system allows private lines to be displayed as dedicated line buttons or “line keys” at each user's telephone instrument at all times. The key system interface is designed to provide two important telephony features for private line functionality:                Continuously display line status indications for each terminated private line (ring, idle, busy) at each user's telephone.        Provide users with equal and simultaneous access to all private line terminations via dedicated buttons.        
No call branching (routing) is utilized by a key system. Termination of the private line and advertisement of the circuit's state is typically displayed on dedicated line buttons at each user's telephone. Users are free to access the circuit for incoming or outgoing calling. Peers are free to join active calls by selecting the active button on their key telephone. FIG. 10 illustrates the interface and display of private line circuits as button appearances on key telephones.
Key telephone systems designed prior to 1980 used physical wiring to connect private lines to each user's key telephone. Modern key telephone systems use switching technology and software to assign telecom services connected on line interface cards to user key telephone devices (turret). While programming private line appearances to user key telephone buttons is no longer physically laborious, it can be a tedious process for IT personnel to manage. This is because trading floors can have hundreds of private lines with hundreds of user telephones that need to be properly assigned to meet each user's unique configuration. This programming step is usually performed by IT staff and not the individual users themselves.
Testing coordination between sites: The provision process is complex as has been shown on the carrier side, customer termination with two different customer sites, line interface termination on two customer sites, line interface programming on two customer sites, and button programming on two customer sites. The complex process involves many different people and is error prone. Therefore, the final required step in the provisioning process is end to end testing.
Testing new private line circuits is usually the responsibility of the customer that initially orders the service connection. The telecom service provider will test for connectivity back to their central office, but the customer is largely responsible for distant party circuit coordination and making test calls to confirm the private line is operational. This process is time consuming and requires tight coordination between customer, telecom service provider and distant end counterparty firm. The following are sequential steps that need to be successfully completed before a newly installed conventional private line can be used.                Distant counterparty approval of telecom service installation        Proper installation of private line circuit at customer site        Proper installation of private line circuit at distant counterparty site        Programming of private line service onto customer key telephone system        Programming of private line service onto user telephone line buttons        Programming of private line service onto counterparty key telephone system        Programming of private line service onto counterparty telephone line buttons        End to end calling on key telephones between customer and counterparty locations        
Currently, there are no automated test processes for private line service deployment. The end to end testing requires manual coordination and careful scheduling between telecom service providers, customer, IT personnel, users and the distant counterparty.
Cost and Logistics: Typical provisioning timeframes for private voice circuits can range from two weeks for intra-city connections to months when the locations are in different cities or even countries. During this period, the trading firms often cannot conduct business. While telecommunications technologies have advanced in the past 40 years from analog to digital TDM to Internet protocols, the provisioning process for private voice circuits has not been modernized.
Because of the logistical complexity and the need to reserve network carrier bandwidth, private voice circuits are costly and often require firms to commit to installation charges, monthly recurring charges and yearly commitments with strong penalties for early disconnect. The dilemma for these firms is that unless they have a long term need to conduct business with another firm it is often not practical for the firm to order private line service. Monthly charges for private voice circuits can range from $50(US) for intra-city connection up to $2,000(US) for inter-country connections. Major financial services firms often have several hundred private lines connecting a single trading location to other financial services firms that they have formal trading relationships with. Thus, this can become a very expensive proposition.
Even with such a great cost, over time, it is not unusual for a private line to be used infrequently. Sometimes it can happen because the user of the private line leaves the firm and takes the counterparty relationship with them, or possibly the user's need was based on a short-term business opportunity. Oddly, it can also be that the counterparty has changed their location and not notified the firm to order a circuit disconnect. In most cases firms do not monitor the activity of their private voice circuits, and users of private lines are not incentivized to notify IT managers if circuits are no longer required. The effect is unnecessary telecom costs creep higher over time as the inventory of private voice circuits are added and users request additional connections related to new business opportunities but do not disconnect old unused circuits.
Conventional private connections cannot be dynamically created. The connections are made between two firms with no way to know how many participants are listening on each end of each connection. The participant(s) on each end connection share the connection and there is no way for a subset of the group to transition to a separate connection for a side conversation both because the group members are not known and because another connection would need to be dynamically setup for the subset to speak on. Dynamic connections are not possible since traditional fixed connections are hard-wired connections that must be manually provisioned.
It would be advantageous to be able to discern the parties who are connected to a private connection. It would also be advantageous to dynamically create a separate connection for a subset of the parties connected to the private connection.